Analog-to-digital converters (ADC) convert analog signals to digital signals. Most ADCs contain feedback loops that are intended to increase the accuracy with which the analog-to-digital conversion occurs. These feedback loops typically contain digital-to-analog converters (DACs) that convert the output of the ADC back to an analog voltage that can be subtracted from the analog signal being input to the ADC, with the goal of this feedback being to make the feedback analog signal equivalent to the input analog signal.
The accuracy of the ADC depends in substantial part on the accuracy with which the DAC elements operate. Many DACs are flawed because the current sources therein produce currents inconsistently—inconsistencies that often arise as a consequence of imperfect manufacturing techniques. To correct for such inconsistent current production, various switches are used in the ADC feedback loop to vary (e.g., randomize) the manner in which current sources are used, resulting in average current values that are more consistent over time. Such switching networks are large, however, and it is thus difficult for them to maintain pace with high-frequency analog input signals.